Abstract

We present a set of Coulomb point charges and van der Waals parameters for molecular dynamics simulations of interfaces between natively deprotonated amorphous SiO2 surfaces and liquid water, to be used in combination with standard biomolecular force fields. We pay particular attention to the extent of negative charge delocalisation in the solid that follows the deprotonation of terminal silanol groups, as revealed by extensive Bader analysis of electronic densities computed by density functional theory (DFT). The absolute charge values in our force field are determined from best-fitting to the electrostatic potential computed ab initio (ESP charges). Our proposed parameter set is found to reproduce the energy landscape of single water molecules over neutral and deprotonated amorphous SiO2 surfaces and, after a minor adjustment, over thin oxide films on Si. Our analysis reveals a certain degree of arbitrariness in the choice of the DFT scheme used as the reference for the force-field optimisation procedure, highlighting its intrinsic limits.

Interaction between a water molecule and an oxidised Si surface calculated with several DFT and force-field schemes, and delocalisation of the negative charge upon deprotonation of an amorphous SiO2 surface.